1. Field of the Invention
The present invention relates generally to apparatus and method for inspecting articles, and particularly to apparatus method for more rapidly and accurately comparing the characteristics of an article being inspected with the characteristics of an ideal sample article with a minimum of stored data.
2. Description of Prior Art
The desirability of electronically comparing the characteristics of a sample article with the characteristics of an article to be inspected has been recognized for some time. To accomplish this, the prior art generally a complete image signal, usually an analogue signal. In some instances the analogue image signal is processed to a digital signal, and in certain instances further processed to record less than the data required to reproduce an image of the subject. The prior art often stores only a "standard" image and compared the image of the article to be inspected with the "Standard" image in real time.
Typical of such prior art concepts are the teachings of U.S. Pat. No. 3,777,169 issued Dec. 4, 1974, and related U.S. Pat. No. 3,598,907, issued August 10, 1971. In this concept, an analogue TV image signal is produced and processed to digital form. Only signals exceeding a threshold voltage are entered into the memory. The stored video pattern from the ideal or previous scan is then compared in real time with a later scan. In the event of lack of comparison, a reject signal is generated.
Other electronic inspection systems include U.S. Pat. No. 3,576,442, issued Apr. 27, 1971 and U.S. Pat. No. 3,746,784, issued July 17, 1973. In general, the prior art inspection systems utilize a video or analogue sensing mechanism, the inspection is generally for impurities or blemishes and accordingly a surplus of data is generated and processed by such means as edge detection systems and suppression systems.